More and more mobile devices are equipped with fingerprint sensors. By acquiring and recognizing user fingerprints, it is possible to distinguish users' identities, so that turning on/off of functions of the mobile devices may be controlled more conveniently. Typically, a scanning circuit scans fingerprint data through the whole area of a touch screen of a mobile device. As the area of the touch screen is large, scanning time is relatively long, and accordingly, power consumption of the scanning circuit is high.